It is well recognized that a dust laden atmosphere in a closed area is a prime condition for a destructive explosion if a spark is struck in the area. Numerous destructive explosions occure in grain elevators because the conditions are just right. Another prime enclosure for destructive explosion events is the grinding or shredding chamber of mills, where trash is shredded by rapidly rotating hammers which generate a high level of sparks.
It is known that in trash collecting and disposal operations, items like paint thinner containers, ether containing bottles, aerosol cans and other containers charged with hydro-carbons are picked up with combustible components. When these collectibles are thrown into a shredder or grinder for reduction by hammers, there is a constant sparking condition. When the conditions are correct an explosion can be created by some component catching fire to act as the detonator for an explosion. Thus, an industrial explosion is set off by rapid propagation of the flame front.
It is known that an industrial explosion, whether it is in a grain elevator, a trash shredder, or other place, is preceeded by rapid pressure increase measured in thousandths of a second before the pressure created by the fire reaches damaging proportions. It is within this very short time period that something needs to be done to quench the fire and flame propagation. The well known Fenwal explosion suppression system was developed to detect pressure rise and release a fire quenching agent into the area where the fire exists. Fenwal is the registered mark of Fenwal Incorporated Division of Walter Kidde & Co., of Ashland, Mass.
The components of substantially all of the Fenwal systems include containers for the suppressing agent which must be maintained under pressure. The containers are provided with blow out rupture discs which release the agent. Since the system is under substantial pressure for rapid delivery of the flame quenching agent, the rupture discs pieces can act as shrapnel and inflict damage to nearby persons. Also the containers are sufficiently heavy to require hoisting equipment for their installation and removal, and superstructure is required to allow persons to reach the sites of the containers. In addition, after an explosive condition has been sensed and the agent bromochloromethane released, it requires a considerable period of time (measured in days) for service people to reach the scene and recharge the system before giving approval for resumption of operations. All of the above is extremely expensive and requires the operation to be shut down. Also, when resetting the system components, the explosive "squibs" used to rupture the discs are dangerous and require the installation of persons trained in the handling thereof.